Historically, poor foam formation in the construction of automotive interior trim components such as instrument pads, door panels, arm rests, glove boxes, center consoles and close out panels has been the foremost cause of scrap and repair related problems in production. These components typically comprise a thermoplastic shell or cover, a metal or plastic retainer and urethane foam to fill the space between the shell and retainer. Urethane foam defects of underfills, voids, ratty foam cell structure, and uneven mix of its components (isocyanate and polyol) is a major manufacturing problem plaguing the entire industry that produces automotive interior trim components of such composite construction. In addition to the manufacturing defects, poor urethane foam formation can cause field failures of the assembled products such as color changes and staining, rough and irregular cover surfaces and cover sinks.
Currently, interior panels such as the instrument panel are typically manufactured using a process called open pouring. In this process, the two halves of a tool called the cavity and lid are opened and foam is poured directly out of a mixhead at low or high pressure onto the backside of the instrument panel shell in general areas. The tool halves are then closed to sandwich the foam between the shell and a retainer with the foam then traveling via blowing agents to fill the open areas. However, a new and improved method has been developed wherein the foam is sprayed onto the entire backside of the shell. This new method is disclosed in U.S. application Ser. No. 08/108,236 filed Aug. 19, 1993, now U.S. Pat. No. 5,389,317, entitled METHOD FOR CONSTRUCTING MOLDED COMPOSITE ARTICLES COMPRISING A SHAPED FOAM CUSHION and assigned to the assignee of this invention. In this method, it is important that the foam be very thoroughly mixed and sprayed onto the shell in a uniform pattern to take full advantage of the improvements available from using this method.
It has been found that conventional mixheads and nozzles are not suited to the task in that the foam components need to be thoroughly mixed and atomized and delivered through a nozzle of extensive length, e.g. as much as about 7 inches, to attain the desired reaching distance so that the tip is approximately 8-12 inches from all the different size mold cavities typically used on a production line. Moreover, the nozzle must then at its tip very evenly or uniformly spray the foam onto the shell. Furthermore, it is important that such a long nozzle be thoroughly flushed with solvent to prevent material buildup both in the nozzle and at its spray tip.